Duplication and expression of CYC2-like genes in the origin and maintenance of corolla zygomorphy in Lamiales.

Summary � Duplication, retention, and expression of CYCLOIDEA2 (CYC2)-like genes are thought to affect evolution of corolla symmetry. However, exactly what and how changes in CYC2-like genes correlate with the origin of corolla zygomorphy are poorly understood. � We inferred and calibrated a densely sampled phylogeny of CYC2-like genes across the Lamiales and examined their expression in early diverging (EDL) and higher core clades (HCL). � CYC2-like genes duplicated extensively in Lamiales, at least six times in core Lamiales (CL) around the Cretaceous–Paleogene (K–Pg) boundary, and seven more in EDL relatively more recently. Nested duplications and losses of CYC2-like paralogs are pervasive but may not correlate with transitions in corolla symmetry. We found evidence for dN/dS (x) variation following gene duplications. CYC2-like paralogs in HCL show differential expression with higher expression in adaxial petals. � Asymmetric expression but not recurrent duplication of CYC2-like genes correlates with the origin of corolla zygomorphy. Changes in both cis-regulatory and coding domains of CYC2like genes are probably crucial for the evolution of corolla zygomorphy. Multiple selection regimes appear likely to play important roles in gene retention. The parallel duplications of CYC2-like genes are after the initial diversification of bumble bees and Euglossine bees.